17 Language support library [support]

17.6 Dynamic memory management [support.dynamic]

17.6.6 Hardware interference size [hardware.interference]

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inline constexpr size_t hardware_destructive_interference_size = implementation-defined;
1
#
This number is the minimum recommended offset between two concurrently-accessed objects to avoid additional performance degradation due to contention introduced by the implementation.
It shall be at least alignof(max_align_t).
[Example 1: struct keep_apart { alignas(hardware_destructive_interference_size) atomic<int> cat; alignas(hardware_destructive_interference_size) atomic<int> dog; }; — end example]
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inline constexpr size_t hardware_constructive_interference_size = implementation-defined;
2
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This number is the maximum recommended size of contiguous memory occupied by two objects accessed with temporal locality by concurrent threads.
It shall be at least alignof(max_align_t).
[Example 2: struct together { atomic<int> dog; int puppy; }; struct kennel { // Other data members... alignas(sizeof(together)) together pack; // Other data members... }; static_assert(sizeof(together) <= hardware_constructive_interference_size); — end example]